The invention relates to an electromagnetic relay having the ability to withstand short-circuit and overload.
Conventional solutions for ensuring short-circuiting and overload strength for a relay predominantly make use of protective means interrupting the load current in case of disturbances, using thermal effects. This includes in particular fuses or bimetal contact springs.
SU 142 74 72 A1 discloses a short-circuit protection for a rotary current motor, which is realized with the aid of reed relays. However, the reed relays are disposed separately from the motor relays there. In particular, with respect to the motor relays which switch on the voltage supply of the motor, there is no enquiry possible as to an overload or short circuit state.
It is the object of the invention to provide an inexpensive, integrated and in particular space-saving solution for a short-circuit- and overload-proof relay, in which in particular a differentiated response of the protective means in case of permanent overload of the relay, and not only in case of short-time current peaks, is desired.
According to the invention, this object is met by an electromagnetic relay comprising
a magnetic system containing an exciting coil through which a control current flows, a core and an armature, with the core and the armature forming at least one operating air gap,
at least one movable contact element and at least one fixed contact element through which one load current circuit each can be closed, coil and contact terminal elements,
a reed contact in each load current circuit, which is coupled to a load current conductor having a load current flowing therethrough, and
means for generating and processing an overcurrent signal and for switching off the control current.
A relay according to the invention is adapted to be reset to a normal operating state by interruption of the control current. In comparison with Hall sensors, which are also suitable for detecting a magnetic field emanating from a raised load current, reed contacts offer the advantages of a temperature-independent behavior, simple adjustment of triggering threshold values and simple realization of evaluation circuits.
Preferred developments concerning the arrangement of the reed contact in relation to the load current conductor, the shielding of the reed contact from the magnetic field of the exciting coil and with respect to the means for generating and processing the overcurrent signal and for switching off the control current are indicated in the dependent claims.